Diet advice in simple parallel structure. 朝を抜く ('to skip breakfast') uses 抜く ('to pull out, to omit') idiomatically — the same construction works for 昼を抜く ('skip lunch') and 薬を抜く ('skip a dose'). 昼を軽くしたら chains an adjectival predicate (軽く + する) with the たら conditional. ~てもよろしい is a slightly formal permission form, よろしい being the polite/formal version of いい. The whole sentence is written in a patterned, slightly lecturing tone.